Kids are kids. They got no idea. I give my kids a mint common set, and they page them. Then they move them around. And play games with them. And scoop them all up and put them back in their binders/pages. Sure...they aren't mint any more, but they're building memories, having fun and growing an affinity for RL and cricket. They enjoy filling gaps in their sets when they built their first set this year. They love lining up and trying to get IP sigs on their scuffy cards that have been in their sweaty hands or pockets all day. They love meeting collectors like Wookie.
And 99.9% of parents buying their kid(s) some footy cards at Coles or the servo ain't gonna know their Authentic Signature card from their common card.